Contribution of the fluorescence to conversion electron yield X-ray absorption fine-structure measurements

摘要

Influence of an extra electron yield induced by the fluorescence process has been experimentally shown and analytically described. Analyse of the conversion electron yield (CEY) signal induced by pure bulk Ag (Ag K edge) and pure bulk Ni or Cu recovered by a thin Fe layer (Ni and Cu K edges) has been performed. This fluorescence electron yield leads to enhancement of the edge height, modification of the shape of the X-ray absorption near-edge structure and decrease of the extended X-ray absorption fine-structure (EXAFS) amplitude. Extrapolation of the model concerning unrecovered bulk samples was carried out in order to explain the EXAFS amplitude reduction often observed in CEY measurements with respect to that obtained in the transmission mode. The reduction Delta chi/chi increases with increasing atomic number Z of the studied element. Delta chi/chi can be considered as negligible for low-Z elements (Ni and Cu). It becomes important for high-Z elements. The k dependence of the amplitude reduction is rather limited and this reduction can be simply explained by a proportional factor. In order to correct this unwanted effect, a theoretical calculation process can be performed or the sample structure can be specially designed to minimize it. Thin films deposited on a substrate consisting of a low-Z element do not generate significantly this extra electron yield. [References: 15]